1. Field of the Invention
The present invention relates generally to the field of wireless communication protocols, and more particularly, to encoding and decoding control information in a Medium Access Control (MAC) Protocol Data Unit (PDU).
2. Description of the Related Art
Broadband wireless networks are based on various communication standards. For example, the Institute of Electrical and Electronics Engineers (IEEE) 802.16e based Worldwide Interoperability for Microwave Access (WiMAX) standard, and its evolution to IEEE 802.16m, provides various types of services such as voice, packet data exchange, and the like.
A connection is established between a mobile station and a base station to exchange service or control information associated with various types of services. The type of connection established between the mobile station and the base station depends on the type of the information to be exchanged. Typically, a control connection is established if control information needs to be exchanged, whereas a transport connection is established when service information exchange. Typically, the service data or control data is exchanged between the mobile station and the base station using MAC PDUs.
The MAC PDU format includes a MAC Header, an Extended Header (EH) group, and payload data. Typically, two types of MAC headers exist, a Generic MAC Header (GMH) and a Short Packet MAC Header (SPMH). Either the GMH or the SPMH is used in the MAC PDU and is negotiated between the base station and the mobile station at the time of connection establishment. The GMH format (based on the IEEE 802.16m standard) includes a flow IDentifier (ID) field, an EH field, and a length field. The SPMH consists of a flow ID field, an EH field, a length field, and a sequence number field.
A connection is identified by the flow ID field. The EH field indicates whether an EH group is present in the MAC PDU. Further, the length field gives information about the length of the MAC PDU. The sequence number field in the SPMH indicates numbering of the transmitted MAC PDUs. The EH group contains an EH group length field and one or more EHs. The EH group length field indicates a length of the EH group in the first byte of the EH group field. Also, each of the one or more EHs includes a type field and a body contents field. The type field indicates a type of EH and the body contents field indicates the type-dependent contents.
Typically, a Length Extended Header (LEH) is encoded in the EH group field when the length of the MAC PDU is greater than 2047 bytes. The presence and absence of a large length field is indicated by the presence/absence of the LEH in the EH group field. When the MAC PDU including the LEH in the EH group field is received by a receiver, the receiver has to parse the EH group field to decode the LEH and determine the 14 bit length field. It is understood that, the 11 bits in the length field in the GMH and the 3 bits of the length field in the LEH together form the 14-bit length field that defines the length of the MAC PDU. Since, this 14-bit length field is not contiguous, processing of the length field in the received MAC PDU may become more complex and hence affect the performance of the receiver.
Additionally, the EH group field may carry variable size EHs. Sometimes, for high data rate connections involving multiplexing information, or when a large number of transport control protocol acknowledgements need to be transmitted, the length information associated with the EHs may exceed the size that can be encoded in the EH length field (e.g., 8 bits). Consequently, efficiency and performance of a wireless communication system may be significantly affected.